Noun
the moment of meeting (of two people, vehicles, etc.); the moment of running into each other; the moment of crossing paths
わたしが前をよく見てなかったから、出会い頭にぶつかっちゃって。小川くんは悪くないわ。Because I wasn't looking where I was going, I bumped into him when we passed. It wasn't his fault.
Also written 出合い頭【であいがしら】